Microreactor-enhanced advanced oxidation for BPS removal: Process intensification, kinetics and toxicity evaluation

Advanced oxidation processes (AOPs) are effective for degrading emerging contaminants but are often constrained by high energy demand and limited control over the formation and persistence of toxic transformation intermediates, which undermines their sustainability in practical applications. Herein, a serpentine microreactor coupled with UVA/TiO₂/g-C₃N₄ nanosheets-activated persulfate system was developed as a cleaner and more controllable treatment strategy for bisphenol S (BPS). Factorial design and modeling analyses identified flow rate and light distance as key parameters governing degradation efficiency. Compared with a conventional batch reactor, the microreactor achieved 94.6% BPS removal with an approximately tenfold higher apparent reaction rate at an equivalent residence time of 34 min, accompanied by more than twentyfold improvement in photocatalytic space-time yield. These improvements reflect more efficient mass transfer, intensified reactant renewal, and uniform photon utilization within the confined microchannels, resulting in improved energy efficiency and process intensification. Time-resolved toxicity evaluation combining Vibrio fischeri bioassays with ECOSAR modeling demonstrated that the microreactor shortened the duration and magnitude of transient ecotoxicity peaks, enabling faster detoxification relative to the batch system. This controllable reaction environment allows precise tuning of residence time for targeted degradation pathways and reduced secondary risks. By providing precise residence-time control and a stable reaction environment, the microreactor facilitates cleaner degradation pathways with reduced secondary environmental risks. This work demonstrates that integrating AOPs with microreactor technology offers a promising route toward cleaner, energy-efficient, and environmentally safer treatment of trace-level emerging contaminants.